Apparatus For Multi-Level Switched-Capacitor Rectification And DC-DC Conversion

ABSTRACT

A voltage-step down rectifier topology suitable for integration on a die of an integrated circuit is described. In one embodiment, a switched capacitor rectifier is provided having an architecture such that an input voltage swing of the switched-capacitor rectifier is a factor N times an output voltage where N depends upon the number of stages such that the switched-capacitor rectifier can provide a π/(2N) step-down voltage conversion ratio between an input fundamental ac peak voltage to the output dc voltage. In one embodiment, the rectifier is used in dc-dc conversion. In one embodiment, the rectifier is used in ac power delivery to low-voltage electronics.

BACKGROUND

As is known in the art, a power conversion circuit (or power converter)is an electrical or electro-mechanical device for converting electricalenergy. One class of power converter is a dc-to-dc converter whichconverts a source of direct current (dc) from one voltage level toanother utilizing inverting and rectifying devices.

As is also known, power conversion becomes more challenging forstate-of-the-art low-voltage electronic circuits, including portableelectronic devices, digital electronics, sensors and communicationcircuits among many items due to the desire of higher voltage conversionratio and rapidly increasing power demand. The size and cost of thepower conversion electronics (such as dc-dc converters) for theseapplications are also important, and can limit overall system design.

As is also known, a buck converter is a step-down dc-to-dc converterwhich utilizes a switched-mode power supply that uses multiple switches,an inductor and a capacitor. Prior art dc-dc converters implementedutilizing conventional buck converters have no transformation stage.Thus, inverting and rectifying devices in such converters are eachexposed to both high current and high voltage signals. This makes suchprior art approaches unattractive for high-conversion-ratio on-die dc-dcconverters.

Referring now to FIG. 1, many conventional dc-dc converters 10 include atransformation stage 12 in addition to inverter 14 and rectificationstages 16. DC-DC converter topologies having a transformation stage(e.g. coupled-inductor buck, flyback, etc.) primarily operate using onlylow-voltage rectifier devices. Furthermore, conventional convertershaving topologies which include a transformation stage requiring coupledmagnetic circuit elements (e.g. transformers) which are difficult tomanufacture on an integrated circuit die and which often have lowefficiency. Moreover, inverter devices used in the aforementionedconventional dc-dc-converter circuits must be capable of fast operationwhile also being able to handle high voltage levels and are unavailablein circuits fabricated using conventional, commercially viableprocessing techniques.

The need for a step-down rectifier as introduced here is driven by theconversion ratio of conventional rectifiers for high-frequencyrectification, which do not provide a desirable step down: from the acvoltage amplitude to the dc output. This places a greater burden on thetransformation stage to achieve a large step-down, and the efficiency amatching network (or other transformer) is often inversely proportionalto the voltage conversion ratio.

For example, and with reference now to FIG. 2, a traditional half-bridgerectifier 20 provides a π/2 voltage conversion ratio between an inputfundamental ac peak voltage to the output dc voltage V_(dc)/V_(ac,pk)(FIG. 2A). This step up in voltage in the rectification stage has theeffect of decreasing the overall conversion ratio in a step down system.If the rectification stage could exhibit step-down characteristics, thenthe voltage transformation ratio in the transformation stage can bereduced while maintaining the same conversion ratio in the system aswhole and hence improve the system performance. A full-bridge rectifierdoubles the input voltage swing and gives a step-down voltage ratio ofπ/4. However, isolation is required for the full-bridge rectifier whichincreases the complexity of the system. As a result, a rectifier withhigher step-down voltage conversion ratio is desired. It should beappreciated that while the half-bridge rectifier of FIG. 2 is here shownimplemented with diodes, such rectifiers are more typically implementedwith CMOS transistors acting as synchronous rectifiers.

SUMMARY

Described herein are new topologies for multi-step, switched-capacitorrectifier circuits including step-down and step-up rectifiers. Therectifiers described herein utilize high step-down ratios which reducesa transformation ratio which must be provided by a transformation stage(which may be implemented with a matching network, transformer, or otherelement). This results in circuits having improved efficiency. Themulti-step, switched-capacitor rectifier circuit topologies describedherein are able to: leverage CMOS devices for rectification and maintainlow blocking voltage for CMOS devices and can be used to construct acpower delivery system and/or GaN/Si dc-dc converters having performancecharacteristics which are improved compared with like characteristics ofprior art systems and converters.

In accordance with the concepts, systems, circuits and techniquesdescribed herein, a multi-step, switched-capacitor rectifier circuitincludes a bridge circuit having an input configured to receive analternating current (AC) signal and a pair of output terminals. Thebridge circuit includes a bridge storage element coupled across theoutput thereof. Bridge circuit switching elements are operable toselectively couple the bridge storage element to the bridge circuitinputs input terminals of a rectifier stage are coupled to the output ofthe bridge circuit. The rectifier stage has a pair of output terminalshaving a rectifier storage element coupled there between with therectifier stage configured to provide an output signal at the pair ofoutput terminals. The rectifier stage further includes control switcheswhich selectively couples the rectifier storage element to the bridgecircuit output.

With this particular arrangement, a multi-step, switched-capacitorrectifier circuit is provided. A switched-capacitor rectifier circuitcomprising a bridge circuit (e.g. a half-bridge circuit) and onerectifier stage functions as a two-step switched-capacitor rectifiercircuit while a switched-capacitor rectifier circuit comprising a bridgecircuit and N rectifier stages functions as an N+1 stepswitched-capacitor rectifier circuit.

In step-down rectification topologies described herein the multi-step,switched-capacitor rectifier circuit utilizes a relatively higherstep-down ratio in the rectifier circuit. This approach reduces thetransformation ratio in the transformation stage (e.g. a transformationratio provided by a transformer or matching network or other type oftransformation network or element), and thus improves efficiency. Whenan input ac current is positive, switches are configured (open orclosed) to connect capacitors such that positive current charges a firstcapacitor provided as part of the bridge stage (i.e. a bridgecapacitor). This current recharges a second capacitor provided as partof the rectifier stage (i.e. a rectifier capacitor) during at least aportion of this state, and this current and the current in the rectifiercapacitor support a load current. Since both the bridge and rectifiercapacitors hold the same voltage Vo at steady-state, the input voltageof the SC rectifier is approximately 2Vo in this state. When the inputcurrent is negative, switches in the bridge and rectifier circuits areconfigured (e.g. either open or closed) such that bridge and invertercapacitors are connected in parallel to support the load and an input ofthe SC rectifier is shorted to a reference potential (typically ground).An additional dc blocking element such as a capacitor may be placed inseries with an input of the rectifier in order to block the dc voltagecomponent at the rectifier input from appearing at circuits driving therectifier.

In step-up rectification topologies, the multi-step, switched-capacitorrectifier circuit utilizes a relatively high step-up ratio in therectifier circuit. This approach reduces the transformation ratio in thematching network, and thus improves efficiency while the voltagetransformation of the whole system maintains the same.

In some embodiments, the bridge circuit is provided as a flyinghalf-bridge circuit while in other embodiments, the bridge circuit isprovided as a full-bridge circuit.

In one embodiment, the multi-step, switched-capacitor rectifier circuitis implemented as a voltage step-down rectifier. The need for astep-down rectifier as described herein is driven by the conversionratio of conventional rectifiers for high-frequency rectification, whichdo not provide a desirable step down from the ac voltage amplitude tothe dc output. This places a greater burden on the transformation stateto achieve a large step-down, and the efficiency a matching network (orother transformer) is often inversely proportional to the voltageconversion ratio.

In one embodiment, the multi-step, switched-capacitor rectifier circuitis implemented as a voltage step-up converter. By driving the rectifierin reverse, the rectifier can operate as an inverter having a largestep-up voltage conversion ratio. When implemented in this manner, thecircuit provides a square wave output signal having a relatively largeamplitude. Although such a voltage step-up rectifier may be consideredmore crude than achievable with other types of inverters (e.g. a Marxinverter), this approach takes advantage of the self-driven nature ofmany of the switches in a CMOS implementation to provide a distinctperformance advantage.

In one embodiment, a multi-step, switched-capacitor rectifier circuitmay be coupled with an inverter and a transformation stage to provide adc-dc converter. In such an embodiment, the rectifier provides a dc-dcconverter having improved voltage transformation capabilities ascompared to conventional converters. The inverter may be realized withhigh-voltage low-current devices (either on the same the as therectifier or a different die) and the transformation stage may berealized with magnetic elements (transformers or inductors) realized onor off the rectifier die. A switched capacitor rectifier driven from aninductive ac source, or an ac source that looks similar to a currentsource having an architecture such that an input voltage swing of theswitched-capacitor rectifier is N times the output voltage dependingupon the number of stages. Hence, the switched-capacitor rectifier canprovide a π/(2N) step-down voltage conversion ratio between the inputfundamental ac peak voltage to the output dc voltage (V_(dc)/V_(ac,pk)).This increases the step down transformation in the rectification stageof a DC-DC or AC-DC power converter.

It has also been recognized in accordance with the concepts, system andtechniques described herein, that future computation systems pose amajor challenge in energy delivery that is difficult to meet withexisting devices and design strategies. Delivery of power to anintegrated circuit die at the final very low voltage requires a dominantportion of the chip pin count that could be better employed forcomputation and communication. Moreover, systems and techniquespresently being used lead to challenges of voltage control (drop) andconductor loss both on die and in interconnect(s) to the die. To reduceinterconnect bottlenecks and enable more flexible computation and energyutilization, it is desired to deliver power across the interconnect athigh voltage and low current with on-die or over-die transformation tolow voltage and high current, while providing localized voltageregulation in numerous zones.

Thus, in accordance with a further aspect of the concepts, systems,circuits and techniques described herein, a multi-step,switched-capacitor rectifier circuit may be incorporated in an ac powerdelivery architecture for low-voltage integrated power delivery. Such anac power delivery system includes an inverter having an input configuredto be coupled to an input source and having an output coupled to aninput of an integrated transformation stage via an interconnectimplemented as a transmission line interconnect (e.g. a distributed L, Ctransmission line). An output of the integrated transformation stage iscoupled to an input of a multi-step, switched-capacitor rectifiercircuit and an output of the multi-step, switched-capacitor rectifiercircuit is configured to provide an output voltage at an output thereof.

When the switched capacitor rectifier is driven from an inductive acsource, or an ac source that looks similar to a current source, an inputvoltage swing of the switched-capacitor rectifier is N times the outputvoltage depending upon the number of stages. And hence, theswitched-capacitor rectifier can provide a n/(2N) step-down voltageconversion ratio between the input fundamental ac peak voltage to theoutput dc voltage (V_(dc)/V_(ac,pk)). This approach reduces (or ideallyminimizes) the step down conversion ratio of a transformation stage inAC power delivery system to provide better performance.

AC distribution in this application has important merits such as:allowing high-voltage and low current distribution; allowing the use oflow-voltage CMOS rectifiers on die; and, in applications including aninverter, enabling the inverter to be placed off die where size and lossare less important and where it can be effectively realized in anon-CMOS device process. An alternative to magnetic transformers forproviding voltage transformation is the use of matching networks orimmittance conversion networks, which require only inductors andcapacitors to realize. With the emergence of high-efficiency,high-power-density integrated inductors at very high frequencies (VHF)practical ac power delivery system may be manufactured.

Accordingly, the multi-step, switched-capacitor rectifier circuitdescribed herein may be used in at least applications relating to dc-dcconversion as well as to ac power delivery to low-voltage electronics.

It should be understood that while circuit and system operation issometimes described herein with approximately 50% duty ratio ofswitching and sinusoidal input currents, it will be appreciated thatother duty ratios, operating characteristics and modes are possible andare considered to be within the scope of the concepts described andclaimed herein. For example, one may switch between the two states withother than 50% duty ratio, and may use duty ratio as a means of control.Duty ratio will affect the relation between the input ac voltage and itsfrequency components and the dc output voltage. The frequency with whichthe rectifier is switched, and the relative phase of the rectifieroperation (with respect to an inverter and/or with respect to the phaseof the input current) may also be used as control mechanisms in a powerconversion system. Likewise, the input current may have variousfrequency content, including harmonics of the fundamental switchingfrequency and dc.

Furthermore, in some embodiments, it is possible to leverage CMOSdevices for rectification, maintain low blocking voltage for CMOSdevices. It is recognized that in at least some applications a trade-offmay be made between the above advantages and higher device count andgreater control complexity.

The circuits, systems and techniques described herein can be used toprovide improved power delivery and conversion (e.g. improved powerdelivery and conversion for microprocessors for example). The circuits,systems and techniques enable power delivery across interconnects athigh voltage and low current. Also, on or over die transformation to lowvoltage/high current can be made with localized adaptive regulation ofvoltage in numerous zones. This results in efficiency and power densitycommensurate with the needed levels of size. The circuits, systems andtechniques described herein are capable of achieving neededtransformation and multi-point regulation.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the concepts, systems and techniques describedherein may be more fully understood from the following detaileddescription of the drawings, in which:

FIG. 1 is a block diagram of a prior art direct current-to-directcurrent (dc-dc) converter;

FIG. 2 is a block diagram of a prior art half-bridge rectifier circuit;

FIG. 2A is a plot of current and voltage vs. phase (in radians) for thehalf bridge rectifier circuit of FIG. 2;

FIG. 3 is a block diagram of a two-step switched-capacitor rectifiercircuit;

FIGS. 3A-3C are a series of waveforms illustrating the operation of thetwo-step switched-capacitor rectifier circuit of FIG. 3;

FIGS. 4 and 4A are a series of block diagrams illustrating operation ofa two-step switched-capacitor rectifier circuit;

FIG. 4B is a series of waveforms illustrating the operation of thetwo-step switched-capacitor rectifier circuit of FIG. 3;

FIG. 5 is a schematic diagram illustrating control details for theswitched-capacitor rectifier of FIG. 3;

FIG. 6 is a block diagram of a multi-step switched-capacitor rectifiercircuit;

FIG. 7 is a schematic diagram illustrating a self-driven scheme for amulti-step, switched-capacitor rectifier circuit;

FIG. 8 is a schematic diagram of a full-bridge multi-step,switched-capacitor rectifier circuit;

FIG. 9 is a block diagram of a polyphase system with a multi-step,switched-capacitor rectifier circuit;

FIG. 10 is a schematic diagram of a discrete full-bridge two-step,switched-capacitor rectifier circuit implemented using diodes;

FIG. 11 is a schematic diagram of an exemplary discrete full-bridgetwo-step, switched-capacitor rectifier circuit;

FIG. 12 is a block diagram of an ac power delivery architecture for adc-dc converter; and

FIG. 13 is a schematic diagram of an exemplary discrete full-bridgetwo-step, switched-capacitor rectifier circuit; and

FIGS. 13A and 13B are a series of waveforms illustrating the operationof the discrete full-bridge two-step, switched-capacitor rectifiercircuit of FIG. 13.

DETAILED DESCRIPTION

Before describing detailed exemplary embodiments of a multi-step,switched-capacitor rectifier circuit, some introductory concepts andterminology are explained.

It should first be appreciated that the concepts, systems, circuits andtechniques described herein related to multi-step, switched-capacitorrectification and power conversion are sometimes described withreference to a multi-step, switched-capacitor rectifier circuit having aspecific number of steps (e.g. a two-step, switched-capacitor rectifiercircuit). Such reference is not intended to be and should not beconstrued as limiting. It is recognized that the multi-step,switched-capacitor rectifier circuit described herein may be providedhaving any number of steps (one or more steps). One of ordinary skill inthe art, after reading the disclosure provided herein, will understandhow to select the number of steps to use in any particular application.

Furthermore, reference is sometimes made herein to multi-step,switched-capacitor rectifier circuitry (or systems utilizing suchcircuitry) described as operating with a specific duty ratio ofswitching and sinusoidal input currents (i.e. a duty ratio of switchingand sinusoidal input currents of approximately 50%). It is recognized,however, that other duty ratios not specifically enumerated herein arealso possible and are within the scope of the concepts, systems,circuits and techniques described herein. It is recognized, for example,that one may switch between two states with other than 50% duty ratio,and may use duty ratio as a means of control. Duty ratio will affect therelation between the input ac voltage and its frequency components andthe dc output voltage. The frequency with which the rectifier isswitched, and the relative phase of the rectifier operation (withrespect to an inverter and/or with respect to the phase of the inputcurrent) may also be used as control mechanisms in a power conversionsystem. Likewise the input current may have various frequency content,including harmonics of the fundamental switching frequency and dc. Oneof ordinary skill in the art, after reading the disclosure providedherein, will understand how to select a duty ratio (or duty ratios) foruse in any particular application. It is recognized, for example, thatone may switch between two states with other than 50% duty ratio, andmay use duty ratio as a means of control. Duty ratio will affect therelation between the input ac voltage and its frequency components andthe dc output voltage. The frequency with which the rectifier isswitched, and the relative phase of the rectifier operation (withrespect to an inverter and/or with respect to the phase of the inputcurrent) may also be used as control mechanisms in a power conversionsystem. Likewise the input current may have various frequency content,including harmonics of the fundamental switching frequency and dc.

It is further recognized, that multi-step, switched-capacitor rectifiercircuitry having operating characteristics and modes not specificallyenumerated herein are possible and are within the scope of the broadconcepts, systems, circuits and techniques described herein.

It should also be understood that reference is sometimes made herein tointegrated circuits (IC's or chips) constructed using specific types ofsemiconductor technology (e.g. complementary metal-oxide-semiconductor(CMOS)). It should be understood that the broad concepts describedherein may be implemented in any type semiconductor technology (i.e.both processes used to implement that circuitry on integrated circuitsas well as the circuitry itself). In some applications, the multi-step,switched-capacitor rectifier circuits described herein find use incircuits and systems implemented using gallium nitride (GaN)semiconductor technology as well as in Gallium Nitride/Silicon (GaN/Si)semiconductor technology. Also, the circuits and concepts describedherein may be implemented using a variety of different material systems(e.g. Silicon CMOS or GaN/Si dc-dc converters) and/or different devicetypes (e.g., Silicon LDMOS/CMOS conversion or HEMT/CMOS conversion).

Reference is also sometimes made herein to particular applications. Forexample, multi-step, switched-capacitor rectifier circuits are sometimesdescribed herein for use with dc-dc converter and ac power deliveryapplications. Such references are intended merely as exemplary shouldnot be taken as limiting the concepts described herein to thoseparticular applications. It should thus be appreciated that themulti-step, switched-capacitor rectifier circuits and concepts describedherein may also find use in other applications. Applications of theserectifiers may include dc-dc converters or ac-dc converters such as forpowering digital logic or devices, rectifiers operating as part ofrectenna devices or as part of wireless power transfer systems,inverters for synthesizing ac outputs from dc inputs, etc.

It should thus be appreciated that, in an effort to promote clarity inexplaining the concepts, reference is sometimes made herein to specificmulti-step, switched-capacitor circuits or specific multi-step,switched-capacitor circuit topologies. It should thus be understood thatsuch references are merely exemplary and should not be construed aslimiting. After reading the description provided herein, one of ordinaryskill in the art will understand how to apply the concepts describedherein to provide specific multi-step, switched-capacitor circuits orspecific switched capacitor circuit topologies.

Reference is also sometimes made herein to circuits having switches orcapacitors. It should be appreciated that any switching elements orstorage elements having appropriate electrical characteristics (e.g.appropriate switching or storage characteristics) may, of course, beused.

Thus, although the description provided herein below explains conceptssought to be protected in the context of a particular circuit or aparticular application or a particular voltage or voltage range, thoseof ordinary skill in the art will appreciate that the concepts equallyapply to other circuits or applications or voltages or voltage ranges.

Referring now to FIG. 3, a two-step (or two-level) switched-capacitorrectifier circuit 30 which is used to illustrate rectifier operationincludes a flying half-bridge circuit 32 coupled to a rectifier stage34. A voltage source 36 (here shown in phantom since it is not properlya part of the two-level switched-capacitor rectifier circuit 30 iscoupled through a capacitor 37 to a pair of input terminals 32 a, 32 bof flying half bridge circuit 32 and a load 38 (also shown in phantomsince it is not properly a part of the rectifier circuit 30) coupled tooutput terminals 34 a, 34 b of rectifier stage 34 and across which isgenerated an output voltage Vo.

The flying half-bridge 32 and rectifier stage 34 each include one ormore switch components and one or more energy storage components. Inthis exemplary embodiment, flying half-bridge 32 includes switches S1,S2 having bias or control terminals coupled to output voltage Vo and anenergy storage component C1, which is here provided a capacitor, coupledacross the bias terminals of the switches S1, S2. In the exemplaryembodiment of FIG. 3, switches S1, S2 are provided as field effecttransistor (FETs) having source, gate and drain electrodes and inparticular transistor S1 corresponds to a P-channel enhancement modemetal oxide semiconductor FET (MOSFET) while transistor S2 correspondsto an N-channel enhancement mode MOSFET where gate electrodes oftransistors S1, S2 are coupled to bias voltages Vo and capacitor C1 hasa first terminal coupled to the drain of transistor S1 and a secondterminal coupled the source of transistor S2 such that voltages Vy andVx are provided at terminals 34 a, 34 b of rectifier stage 34.

The intermediate voltage Vx is provided at a node of the flyinghalf-bridge 32 and is controlled by rectifier switching elements suchthat said bridge switching elements can be self-driven by an outputvoltage of the rectifier.

Rectification stage 34 includes switching elements S3, S4, S5 and astorage element C2 coupled across rectifier stage output terminals 34 c,34 d. Since the multi-step, switched-capacitor rectifier circuit doesnot require any magnetic circuit elements, the multi-step,switched-capacitor rectifier circuit has a topology suitable forintegration on-die in complementary metal oxide semiconductor (CMOS) andother semiconductor technologies. And while the elimination of themagnetics is major factor in allowing on-die integration (since there isno efficient way to make integrated magnetics using currentstate-of-the-art technology), other features in the topology help forthe on-die integration including, but not limited to, the self-drivenfeature which enables the use of circuits (e.g. switch circuits) whichdo not require the use of external capacitors for bootstrap/flying gatedrivers. Another feature which facilitates/enables on-die integration isthat a flying capacitor (e.g. capacitor C1 in FIG. 5 below) is used as abootstrap capacitor as well for the gate driver referenced to the outputvoltage. This allows elimination of another external capacitor whichwould otherwise be required.

Moreover, the approach described herein allows a conversion with alarge-amplitude input voltage using only low-voltage switch devices andcapacitors, making it further suited to efficient implementation inCMOS. It will be appreciated that the present design using a pluralityof low-voltage switch devices can be more efficient and more easilyimplemented in low-voltage processes than a design requiringhigh-voltage switch devices.

In the exemplary embodiment of FIG. 3, the multi-step,switched-capacitor rectifier circuit is implemented as a voltagestep-down rectifier. The need for a step-down rectifier as describedherein is driven by the conversion ratio of conventional rectifiers forhigh-frequency rectification, which do not provide a desirable step downfrom the ac voltage amplitude to the dc output. This places a greaterburden on the transformation state to achieve a large step-down, and theefficiency a matching network (or other transformer) is often inverselyproportional to the voltage conversion ratio.

In other embodiments, however, the multi-step, switched-capacitorrectifier circuit is implemented as a voltage step-up rectifier. Bydriving the rectifier in reverse, the rectifier can operate as aninverter having a desired (and relatively large) step-up voltageconversion ratio using only low-voltage switches and capacitors. Thesize of the step-up ratio depends upon the number of steps (or levels)included in the rectifier circuit and, basically is the reciprocal ofthe step-down ratio. Thus, for step up circuit operation, the ratiobecomes (2N)/π. From the description provided herein, it should beappreciated that a minimum of two steps or levels are required toprovide a step-up ratio. When implemented in this manner, the circuitprovides a square wave output signal having a relatively largeamplitude. This is accomplished while only requiring switch devices andcapacitors having a small voltage rating. Although such a voltagestep-up inverter may be considered more crude than achievable with othertypes of inverters (e.g. a Marx inverter), this approach takes advantageof the self-driven nature of many of the switches in a CMOSimplementation to provide a distinct performance advantage (i.e. nofloating drivers are required and the floating/flying switches areself-driven).

A controller circuit (not shown in FIG. 3) provides control signals toswitching elements S3, S4, S5 through driver circuits to provide desiredoperation as will be described in below in conjunction with FIGS. 4-4B.Suffice it here to say that rectifier circuit 34 operates such that acontrolled voltage (either a step-down or a step-up voltage) is providedas output terminals thereof. An exemplary driver circuit will bedescribed hereinbelow.

It should be appreciated that the topology for step-down rectificationdescribed herein allows use of a step-down ratio in the rectifiercircuit which is relatively high compared with step-down ratios inconventional circuits. Conventional half bridge rectifiers, for example,have a step-down ratio of (π/2)—greater than one—between the input acfundamental voltage to the dc output voltage.

In the multi-step, switched-capacitor rectifier described herein,however, it is possible to achieve a (π/(2N)) step-down voltageratio—less than one for two or more steps—where the precise ratiodepends upon the number of steps (or levels) included the rectifiercircuit. The step-down ratio achieved is said to be relatively largecompared with conventional approaches since it is possible to have astep-down ratio much smeller than 1 if the rectifier circuit includes alarge number of levels. The voltage step-down system includes a matchingnetwork and a rectifier (from ac to dc). While maintaining the overallsystem voltage step-down ratio the same, either the rectifier or thematching network provides the voltage step down. For the matchingnetwork, the efficiency is an inverse function of the transformationratio. The higher transformation ratio needed in the matching network,the lower efficiency it will be.

The approach described herein reduces the transformation ratio in thematching network, and thus improves efficiency.

Furthermore, in some embodiments, it is possible to leverage CMOSdevices for rectification, maintain low blocking voltage for CMOSdevices. It is recognized that in at least some applications a trade-offmay be made between the above advantages and higher device count andgreater control complexity.

Referring now to FIGS. 3A-3C, waveforms of the two-levelswitched-capacitor rectifier circuit 30 of FIG. 3 are shown. Thewaveforms illustrate operation of the rectifier circuit. It should benoted in FIG. 3B that the input of the rectifier switches betweensubstantially 0 volts and substantially 2Vo volts, and a step down ratioof π/4 is provided between an input ac fundamental voltage to dc outputvoltage in the two step SC rectifier. This step down is achieved usingdevices that only need to be rated for the (small) output voltage, andnot the peak of the (large) input voltage.

Referring now to FIGS. 4 and 4A, switch operation of the two-levelswitched-capacitor rectifier circuit 30 of FIG. 3 is described. Withreference first to FIG. 4, when the input ac current is positive,switches labeled S1 are closed and switches labeled S2 are open. Thecapacitors C1 and C2 are connected such that positive current chargescapacitor C1. This current recharges C2 during at least a portion ofthis state, and this current and the current in C2 support the loadcurrent. Since capacitors C1 and C2 both hold the same voltage Vo atsteady-state, the input voltage of the SC rectifier is approximately 2Voin this state. Thus, the input voltage of the SC rectifier during oneswitch state is substantially 2Vo.

When the input current is negative, switches S1 are opened and switchesS2 are closed. In this case, capacitors C1 and C2 are connected inparallel to support the load and the input of the SC rectifier isshorted to the ground. As a result, the input voltage of the SCrectifier is 0 volts (V). In this case, it has a 2Vo voltage swing atthe input of a rectifier, thus providing aV_(dc)/V_(in, fundamental)=1/(4/π)=π/4 fundamental peak ac-to-dcconversion which results in step-down in the rectification stage. Higherlevel versions of this switched-capacitor rectifier can provide a higherstep-down ratio, but require a higher device count and greater controlcomplexity.

The switched-capacitor rectifier operation described above illustratesthat all devices in the rectifier circuit need only block the low outputvoltage level since they are only required to block the voltages acrossthe capacitors. As a result, the rectifier can be implemented utilizinglow voltage CMOS devices. This results in a circuit having lowerswitching loss and/or higher switching frequency (i.e., input acfrequency) at a given efficiency as compared to designs requiring highvoltage devices. For example, in a designs operating at a few voltsoutput, ac frequencies of 10 MHz, 20 MHz or even 50 MHz are achievableat high efficiency. For designs at output voltages of 2 V and below, acfrequencies in the VHF range such as 30 MHz, 50 MHz or even 100 MHz areachievable. As switching element S3 has its control part referenced to adc output voltage (i.e. switching element S3 sits on top of DC outputvoltage), it can be driven easily. Also, switching elements S1 and S2can be self-driven by the output voltage. A detailed control circuit forthe two-step switched-capacitor circuit of FIG. 3 is described inconjunction with FIG. 5.

Referring now to FIG. 4B, a series of waveforms illustrate thetheoretical switching and voltage waveforms of the two-stepswitched-capacitor rectifier circuit of FIG. 4. Intermediate voltageV_(x) switches between 0 and V_(o) volts while V_(y) switches betweenV_(o) to 2V_(o) volts and V_(in) switches between 0 to 2V_(o) volts.Thus, the circuit provides an additional factor of two step downcompared to a half-bridge while maintaining device and capacitor stressat a voltage level of V_(o).

Although this example utilizes a duty ratio of 50% (i.e. a duty ratio ofswitching and sinusoidal input currents of approximately 50%), it isrecognized that other duty ratios not specifically enumerated herein arealso possible and are within the scope of the concepts, systems,circuits and techniques described herein. It is recognized, for example,that one may switch between two states with other than 50% duty ratio,and may use duty ratio as a means of control. Duty ratio will affect therelation between the input ac voltage and its frequency components andthe dc output voltage. The frequency with which the rectifier isswitched, and the relative phase of the rectifier operation (withrespect to an inverter and/or with respect to the phase of the inputcurrent) may also be used as control mechanisms in a power conversionsystem. Likewise the input current may have various frequency content,including harmonics of the fundamental switching frequency and dc. Oneof ordinary skill in the art, after reading the description providedherein, will understand how to select a duty ratio (or duty ratios) foruse in any particular application. It is recognized, for example, thatone may switch between two states with other than 50% duty ratio, andmay use duty ratio as a means of control. Duty ratio will affect therelation between the input ac voltage and its frequency components andthe dc output voltage. The frequency with which the rectifier isswitched, and the relative phase of the rectifier operation (withrespect to an inverter and/or with respect to the phase of the inputcurrent) may also be used as control mechanisms in a power conversionsystem. Likewise the input current may have various frequency content,including harmonics of the fundamental switching frequency and dc.

Referring now to FIG. 5, a control circuit for the multi-step,switched-capacitor rectifier of the type described above in conjunctionwith FIGS. 3-4B is shown. A flying capacitor C1 can he used as abootstrap capacitor to provide energy for the gate driver of switchingelement S3. This eliminates extra circuitry which may otherwise berequired to supply power for the gate driver of switching element S3 andalso reduces (and ideally minimizes) the energy storage capacitance ofcapacitor C3. In addition, since switching elements S1, S2, S3 and S4share the same control pattern, only a constant voltage (illustrated asVo in the exemplary embodiment of FIG. 5) is required to drive the gateof switching elements S1 and S2 while the node at which voltage Vxappears can be controlled by switching elements S4 and S5. As a result,the first stage switching elements S1 and S2 can be self-driven byoutput voltage V_(o) as illustrated in the exemplary embodiment of FIG.5.

It should be appreciated that the multi-step, switched-capacitorrectifier utilizes a clock circuit which provides non-overlapping pulses(i.e. a non-overlapping clock generator may be used). With thecontrolled dead-time (non-overlapping gap), the input current candischarge/charge the output capacitance in the switches to achieve azero-voltage switching scheme (similar to class-D or class DEoperation). In this case, switching loss due to device outputcapacitance can be reduced (and ideally eliminated) resulting inimproved rectifier efficiency. In addition, the gate driver can be madeweaker (the transition time can be longer due to lower switching loss)to reduce the loss in the gate driver.

Referring now to FIG. 6, a general structure of a multi-step,switched-capacitor rectifier circuit 50 includes a plurality of, here N,rectifier stages 52 a-52N. A half flying bridge 64 is coupled between asource 56 and a first one of the N rectifier stages and a load 58 iscoupled to an output of the Nth rectifier stage.

It should be appreciated that this rectifier is ideally driven from aninductive ac source, or an ac source that looks similar to a currentsource (this is because the input voltage of the rectifier is switchingand controlled by the operation of the rectifier, and thus the rectifieris best driven by a current source, rather than a voltage source).

Except for the switches SB coupled to the top of the half bridges, allother switches can be replaced by diodes. In steady state operation, thevoltages across all capacitors are equal to the output voltage. Whetherthose capacitors will be connected in series or in parallel by theoperation of the switches depends upon the current direction. With thisconfiguration, the input voltage swing of the switched-capacitorrectifier is N times the output voltage where N corresponds to thenumber of stages. And hence the switched-capacitor rectifier can providea π/(2N) step-down voltage conversion ratio between the inputfundamental ac peak voltage to the output dc voltage (V_(dc)/V_(dc,pk)).This Increases the step down transformation in the rectification stageof a dc-dc or ac-dc power converter and also minimizes the step downconversion ratio of a transformation stage in an ac power deliverysystem (to be discussed hereinbelow in conjunction with Fig.) to providebetter performance.

It will also be recognized that this rectifier can be driven in reverseto provide an inverter having a large step-up voltage conversion ratio.When implemented in this manner, one gets a large amplitude square waveoutput. Although this is more crude than achievable with a Marxinverter, for example, this approach takes advantage of the self-drivennature of many of the switches in a CMOS implementation to provide adistinct performance advantage.

Referring now to FIG. 7, a driving scheme of a multi-step SC rectifier(e.g. as described above in conjunction with FIG. 6) is shown. Ingeneral, devices in the bridge of a previous stage or level (e.g. stage62P-1) can be driven by a positive voltage of the capacitor in the nextstage or level (e.g. stage 62P).

Furthermore, the devices referencing to the positive node of the flyingcapacitors can be driven by a dc voltage (N)(Vo) where N corresponds tothe level at which the device is located in the circuit) since theirreference nodes are switching with the flying capacitors. This approachgreatly reduces the complexity of the driving scheme.

Only the devices in the last stage are required to be controlled and allother devices in the multi-step SC rectifier can be either self-drivenor driven by a dc voltage.

Referring now to FIG. 8, a multi-step, switched-capacitor rectifiercircuit 66 implemented with two bridge stages operating in complementaryfashion. Each of the bridge stages are provided as half-bridges havingtheir own capacitors (it should be noted that the two bridge stages donot form a full bridge since the respective capacitors are not connectedin parallel). The SC rectifier has the same general operating pattern asa half-bridge SC rectifier (e.g. as described above in conjunction withFIGS. 3-7, for example. This exemplary embodiment, however, has twohalf-bridge SC rectifiers in operating complementary fashion (i.e.operating 180 degrees out of phase). In the this exemplary embodiment ofthe SC rectifier, the input voltage swing is +/−(N)(Vo) so the step-downvoltage conversion ratio is π/(4N). Moreover, no dc voltage component isprovided at the input to the rectifier in this implementation. Thus,similar to the full bridge rectifier, the multi-step, SC rectifier canalso be connected as a full bridge as a way to double its voltage in theinput and convert power from both polarities.

Referring now to FIG. 9, a polyphase version of a multi-step,switched-capacitor rectifier may be constructed and the systemarchitecture is shown in FIG. 9. The circuit includes 78 includes apolyphase inverter 72 having an input configured to coupled to an acsource 74 (shown in phantom since it is not properly a part of thecircuit 70) and an output coupled to an input of a transformation stage76. In one embodiment, the polyphase inverter may be provided as athree-phase GaN inverter. The transformation stage may include, forexample on die magnetic elements. These on-die magnetic elements maypreferably be implemented as inductors, although in some cases coupledmagnetic devices (such as transformers) may be used.

An output of the transformation stage is coupled to an input of apolyphase SC rectifier circuit 78 having a storage element coupledacross an output thereof (with the storage element here beingillustrated as capacitor C). An output voltage Vo is provided across aload 80 (shown in phantom since it is not properly a part of the circuit70) coupled to an output of the SC rectifier circuit 70.

Referring now to FIG. 10, to further explore the functionality of theswitched-capacitor rectifier circuit and validate the concepts andtechniques described herein, an exemplary two stage full-bridgeswitched-capacitor rectifier circuit 84 was fabricated utilizingdiscrete components. The topology of the rectifier circuit 84 isillustrated in FIG. 10. The discrete rectifier circuit was designed foroperating at a 10 MHz switching frequency and a 3V output voltage inmagnitude with 2 W of output power. In order to simplify the control ofthis exemplary prototype embodiment, diodes are used in the bridges. Inaddition, the output voltage polarities are inverted for better PCBlayout purpose (it is noted, however, that this does not affect theoperation of the SC rectifier).

In the exemplary embodiment, the diodes were provided as BAT60A Infineonsilicon Schottky diodes. Switches were provided as Si1012R N-Channelsilicon MOSFET (Vishay) and the drivers for the switches were NC7WZ04TinyLogic inverter manufactured by Fairchild Semiconductor. Isolation isprovided by a 1:1 transformer having a BLN1728-8A/94 core. There are sixturns on the transformer providing magnetizing inductance L_(m) of 961nH and leakage Inductance L_(l) of 43 nH. A 360 nH Coilcraft air coreinductor and a 500 pF ATC capacitor are used to form a matching networkto match the input impedance of the SC rectifier to a 50 ohm (Ω) outputimpedance of a power amplifier.

Referring now to FIG. 11, an integrated rectifier circuit 90 forpolyphase ac power delivery operates with a 2.5V output voltage,designed for 50 MHz switching frequency. The circuit can implementsingle or polyphase systems, can be configured as a 3-phase rectifierand can be configured into three separate full-bridge rectifiers. Thecircuit allows 2 W output power for each phase and thus a total of 6 Woutput power for the system. The system includes a full bridgeswitched-capacitor rectifier capable of providing 4 W output power (itshould be noted that only 1 phase rectifier and half bridgeswitched-capacitor rectifier are shown in FIG. 11).

For an integrated three-phase rectifier, three-phase gate signals arecontrolled with voltage controlled delay lines, a taper factor of 8 isused for the gate driver, 1 ns dead-time is used to achievezero-voltage-switching (ZVS) and two single bridges in parallel areprovided for each phase. Thus, IC 90 includes nonoverlapping clockgeneration circuitry as well as tapered drivers.

As noted above a multi-step, switched-capacitor inverter circuit may beused to provide an ac power delivery system as will be described belowin conjunction with FIG. 12.

Referring now to FIG. 12, an ac power delivery system 100 is coupledbetween a source 102 and a load 104 (with source 102 and load 104 shownin phantom since they are not properly a part of the power deliverysystem 100). Power delivery system 100 includes a very high frequency(VHF) inverter 106 having an input configured to accept a VHF so signalfrom source 102 and having an output coupled to an integratedtransformation stage 110 via a transmission line interconnect circuit108. The integrated transform stage 110 has an output coupled to anon-die rectifier 112 (i.e. a multi-step, switched-capacitor rectifiercircuit). System 100 thus provides ac delivery across an interconnect athigh voltage with local transformation and rectification. It should benoted that high-voltage inverter can be remote and the rectifier can uselow-voltage on-die Si devices. This approach mitigates interconnectthermal and transient limits. With this approach, an ac power deliveryarchitecture for low-voltage integrated power delivery is provided.

It has been recognized that future computation systems pose a majorchallenge in energy delivery that is difficult to meet with existingdevices and design strategies. Delivery of power to the the at the finalvery low voltage requires a dominant portion of the chip in count thatcould otherwise be better employed for computation and communication.Moreover, conventional systems pose challenge related to voltage control(drop) and conductor loss both on die and the interconnect to the die.

It has been further recognized in accordance with the concepts, systemsand techniques described herein, that to reduce interconnect bottlenecksand enable more flexible computation and energy utilization, it isdesired to deliver power across the interconnect at high voltage and lowcurrent with on- or over-die transformation to low voltage and highcurrent, while providing localized voltage regulation in numerous lanes.With the high-voltage ac distribution architecture, high-voltagediscrete power devices (e.g., GaN RF transistors) can be used for theVHF inverter stage off die, generating high-voltage, low-current powerat VHF frequencies (e.g. 50-100 MHz) which is delivered across theinterconnect.

To accomplish this, a transformation network disposed on an integratedcircuit die is used (e.g. disposed on a CMOS). This can be implemented,for example, by using integrated passive circuit elements (a/k/a“passives”) on a CMOS die to form a matching network for thetransformation stage. This converts the VHF power to low voltage andhigh current.

Integrated rectifiers of the type introduced here, using nativelow-voltage CMOS devices, transform the waveforms back to dc, completingthe power delivery system. This limitation aside, ac distribution inthis application has important merits: it allows high-voltage and lowcurrent distribution, allows the use of low-voltage CMOS rectifiers ondie, and enables the inverter to be placed off die where size and lossare less important and where it can be effectively realized in anon-CMOS device process. One alternative to magnetic transformers forproviding voltage transformation is the use of matching networks orimmittance conversion networks, which require only inductors andcapacitors to realize. Practical ac power delivery systems may includehigh-efficiency, high-power-density integrated inductors which operatein the very high frequency (VHF) range.

Referring now to FIG. 13, an exemplary embodiment of a multi-step,switched-capacitor full bridge rectifier circuit is shown. FIGS. 13A,13B illustrate plots of switched capacitor rectifier system inputvoltage and switched capacitor rectifier voltage, respectively, for thecircuit of FIG. 13. The circuit operates at an 8:1 conversion ratio witha 20 V_(pk,in) ac input, 2.5V dc output and 4 W output power. AC inputline-line voltage amplitude=40 V. A 1:1 hand-wound transformer is usedto provide isolation (BLN1728-8A/94 core, 7 turns, L_(m)=1.2 uH andL_(leak)=30 nH). A 360 pF capacitor is used to resonate out leakageinductance and capacitor C (180 pF) and inductors L (22 nH) are used toform a matching network.

The apparatus and techniques described herein are not limited to thespecific embodiments described. Elements of different embodimentsdescribed herein may be combined to form other embodiments notspecifically set forth above. Other embodiments not specificallydescribed herein are also the scope of the following claims.

What is claimed is:
 1. A multi-step, switched-capacitor rectifiercomprising: a bridge stage having an input adapted to be coupled to afirst source and an output, said bridge stage having a bridge capacitorand at least one bridge switching element coupled between a firstterminal of said bridge capacitor and the bridge input and at least oneswitching element coupled between a second terminal of said bridgecapacitor and the bridge input; and one or more rectifier stages with afirst one of the one or more rectifier stages having an input adapted tobe coupled to an output of said bridge stage and at least one of saidone or more rectifier stages having an output adapted to be coupled to aload and each of said one or more rectifier stages having a rectifiercapacitor and a plurality of rectifier switching elements with at leastone of said rectifier switching elements coupled between a firstterminal of said rectifier capacitor and a first input terminal of therectifier stage, at least one switching element coupled between a secondterminal of said rectifier capacitor and the first input terminal ofsaid rectifier stage and at least one switching element coupled betweena second terminal of said rectifier capacitor and a second inputterminal of the rectifier stage.
 2. The multi-step, switched-capacitorrectifier of claim 1 wherein in response to a positive ac current beingprovided to the input of said bridge circuit, said at least one bridgeswitching elements and said plurality of rectifier switching elementsare configured to connect said bridge capacitor and said rectifiercapacitor such that positive current charges said bridge capacitor andrecharges said rectifier capacitor.
 3. The multi-step,switched-capacitor rectifier of claim 1 wherein both said bridge andrectifier capacitors hold substantially the same voltage Vo atsteady-state.
 4. The multi-step, switched capacitor rectifier of claim3, wherein the input voltage of the SC rectifier during one switch stateis substantially 2Vo.
 5. The multi-step, switched-capacitor rectifier ofclaim 1 wherein in response to a negative ac current being provided tothe input of said bridge circuit, each of said at least one bridgeswitching elements and said plurality of rectifier switching elementsare configured such that said bridge and inverter capacitors areconnected in parallel to support the load.
 6. The multi-step,switched-capacitor rectifier of claim 1 wherein an input voltage swingof the multi-step, switched-capacitor rectifier is N times the outputvoltage where N corresponds to the number of stages in the switchedcapacitor rectifier.
 7. The multi-step, switched-capacitor rectifier ofclaim 1 comprising a single rectifier stage having an input adapted tobe coupled to an output of said bridge stage and having an outputadapted to be coupled to a load, said single rectifier stage having arectifier capacitor and a plurality of rectifier switching elements withat least one of said rectifier switching elements coupled between afirst terminal of said rectifier capacitor and a first input terminal ofsaid single rectifier stage, at least one switching element coupledbetween a second terminal of said rectifier capacitor and the firstinput terminal of said single rectifier stage and at least one switchingelement coupled between a second terminal of said rectifier capacitorand a second input terminal of said single rectifier stage.
 8. Themulti-step, switched-capacitor rectifier of claim 7 wherein said aninput voltage swing of the multi-step, switched-capacitor rectifier is Ntimes the output voltage where N corresponds to the number of stages inthe switched capacitor rectifier.
 9. The multi-step, switched-capacitorrectifier of claim 9 wherein said bridge stage is a CMOS half-bridge,and wherein a first one of the one or more rectifier stages comprises aCMOS half bridge connected across the rectifier output and an additionaln-channel transistor connected between the rectifier output and an inputterminal of said rectifier stage.
 10. The multi-step, switched-capacitorrectifier of claim 1 wherein a constant voltage is used to drive thecontrol terminals of said bridge switching elements.
 11. The multi-step,switched-capacitor rectifier of claim 1 wherein a bridge capacitor ofsaid bridge stage provides energy for a gate driver of a switchingelement in at least one of said rectifier stages;
 12. The multi-step,switched-capacitor rectifier of claim 1 wherein a node at Which anintermediate voltage Vx is provided is controlled by rectifier switchingelements.
 13. The multi-step, switched-capacitor rectifier of claim 1Wherein at least one of the said at least one bridge switching elementsis self-driven by an output voltage of the rectifier.
 14. Themulti-step, switched-capacitor rectifier of claim 1 further comprising anon-overlapping clock circuit.
 15. The multi-step, switched-capacitorrectifier of claim 1 disposed on a die.
 16. The multi-step,switched-capacitor rectifier of claim 1 having said rectifier switchingelements disposed in a complementary metal oxide semiconductor (CMOS)semiconductor circuit.
 17. The multi-step, switched-capacitor rectifierof claim 1 used in dc-dc conversion.
 18. The multi-step,switched-capacitor rectifier of claim 1 used in ac power delivery tolow-voltage electronics.
 19. The multi-step, switched-capacitorrectifier of claim 5 further comprising a transformation stagecomprising one or more magnetic circuit elements provided on or off adie on which the rectifier switching elements are provided.
 20. Therectifier of claim 11 wherein said magnetic circuit elements areprovided as at least one of one or more transformers or one or moreinductors.
 21. A multi-step, switched-capacitor rectifier comprising: abridge stage having an input adapted to be coupled to an input of theswitched-capacitor rectifier and an output, said bridge stage having abridge capacitor and at least one bridge switching element coupledbetween a first terminal of said bridge capacitor and the bridge inputand at least one switching element coupled between a second terminal ofsaid bridge capacitor and the bridge input; and N−1 rectifier stageswith a first one of the N−1 rectifier stages having an input adapted tobe coupled to an output of said bridge stage and at least one of saidN−1 rectifier stages having an output adapted to be coupled to a loadand each of said N−1 rectifier stages having a rectifier capacitor and aplurality of rectifier switching elements with at least one of saidrectifier switching elements coupled between a first terminal of saidrectifier capacitor and a first input terminal of the rectifier stage,at least one switching element coupled between a second terminal of saidrectifier capacitor and the first input terminal of said rectifier stageand at least one switching element coupled between a second terminal ofsaid rectifier capacitor and a second input terminal of the rectifierstage and wherein the multi-step, switched-capacitor rectifier isprovided having an architecture such that an input voltage swing of themulti-step, switched-capacitor rectifier is N times an output voltage.